Apparatus for making lithograph blankets



Feb. 24,1953 w. H. SMITH 2,629,324

APPARATUS FOR MAKING LITHOGRAPH BLANKETS Original Filed Nov. 17. 1947 2SHEETS-SHEET l Feb. 24,

w. H. SMITH 2,629,324

APPARATUS FOR MAKING LITHOGRAPH BLANKETS Original Filed Nov. 1?. 1947lil l i i i i l iil l i Patented Feb. 24, .1953

APPARATUS FOR MAKING LIT-HOGRAPH BLANKETS Walter H. smith, Toronto,Ontario, Canada; Mary Agnes Johnston, adjministratrix of said Walter H.Smith, deceased, assignor to Commercial Lithograph Company, Ltd.,Toronto,

Ontario, Canada Original application November 17, 1947, Serial N0.7863519. Divided and this application April 23, 1949, Serial No.89,261

8 Claims. (Cl. 101415.1)

This invention relates to lithograph blankets and to a method and meansfor making the blanket.

This application is divided out of application Serial No. 786,519, filedNovember 17, 1947, now Patent No. 2,525,003. l

The present day lithograph blankets are all made of canvas-backed rubbersheeting. The thickness of these blankets is not uniform andfurthermore, allof these blankets have a tend ency to stretch so thatthey lack uniformity in use even though their thickness may bereasonably uniform.

In an effort to obtainuniformity inthickness it hasbeen proposed thattheir surfaces be ground down so that they will be even.

To perform this grinding operation the blanket is normally positioned ina plane and a grinding tool passed thereover to removethe high spots onthe surface. This method has proved ineffective, however, due to theelasticity of the rubber as the excess rubber in the high spots has atendency to be pushed in front of the grinding tool and then snappedback beneath so that the resultant surface is uneven. Further, when agrinding wheel is employed, the pull of the wheel forces the rubberahead of it for a short distance so thatan uneven surface is created,even if it were not uneven in the beginning.

It is absolutely essential that a lithograph blanket have asubstantially uniform thickness as this blanket is the actual printingmember. In the usual offset lithograph press, a printing plate iswrapped around a printing cylinder, and the rubber lithograph blanket iswrapped around an impression cylinder which is juxtaposed relative tothe printing cylinder, so as to transfer an image from the printingplate to the rubber sur face of the blanket whichin turn offsetsorprints the received image on a sheet of paper or other sheetmaterialsuch as tin, foil, and the like.

There can be no unnecessary pressure exerted betweenthe blanket andeither the printing plate or the paper sheet except for the merepressure of contact that is necessary and which may be in theneighborhood of of an inch squeeze. As the entire surface of the blanketmust be well known methods of attaching, and stretched taut by thepressman. An impression is pulled between the plate, which for thispurpose is inked solid all over the printing surface, and the rubbercovered cylinder, using slightly less pressure during this operationthan the required ultimate pressure in the regular printing operation.This results only the high spotsof the blanket becoming inked. Thepressman then removes the blanket and with paste and thin paper, hepastes sufficient layers of paper under the low spots to bring them upto the high spots. This is known as make ready and requires considerablemanual labor and time on a large press, as much as several hours whenaccurate color work is to berun. After several tests, all the low spotsare built up so that there is an even inking of the blanket. Naturally,if there are no low spots this is eliminated.

Furthermore, the thickness of the prior art blankets occupies anundesirably large amount of space in being attached to certain types ofimpressed into contact with the sheetto be printed,

pression cylinders, such as that disclosed in my Patent No. 1,949,132,sothat the size of the actual printing surface is limited.

Having in mind the defects of the prior art lithograph blankets andmethods for making such blankets, it is an object of the presentinvention to provide an absolutely non-stretchable rubber surfacedblanket.

It is another object of the invention to provide a rubber surfacedlithograph blanket of uniform thickness. l

It is still another object of the invention to provide a lithographblanket having a greater printing area for the given size of the blanketon certain types of impression cylinders as hereinbefore noted. 1

It is a further object of the invention to provide a method forproducing a rubber surface lithograph blanket and for grinding therubber surface of the blanket touniformity. It is :a further object ofthe invention to provide means for mounting and holding a rubbersurfaced blanket upon an arbor or cylinder. 1

The foregoing objects, and others ancillary thereto which will becomeapparent from the following description, are preferably accomplished byalithograph blanket comprising a rubbersheet secured to a thin sheetmetal backing so that the metal backing will preclude the possibility ofstretching and will occupy less space when mounted on an impressioncylinder so as to provide a greater printing area for a given size ofblanket. This blanket may be ground to absolute uniform thickness bymounting tightly aroun a cylinder or arbor with the rubber facingoutward. The arbor may then be mounted in any of the many grindinglathes or machines which can be used for grinding cylindrical surfaces.With the rubber held tightly on a cylindrical form it does not give orstretch in front of the grinding tool as is the case when it is fiat. Adevice for mounting the blanket on the arbor may comprise a cylinderhaving means for gripping the ends of the metal backing, one of saidmeans being movable relative to the other to pull the blanket tight- 1yagainst the cylindrical surface. The arbor may be movably mounted in astandard including a friction roller for rubbing against the outerrubber surface of the blanket to pull it tightly on the cylinder as thecylinder is rotated. This friction roller may be movably mounted to andfrom the cylinder and have a clutch mechanism for adjusting thefrictional resistance of the roller.

The novel features that are considered characteristic of the inventionare set forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of specificembodiments when read in connection with the accompanying drawings,wherein like reference characters indicate like parts throughout and inwhich:

Fig. 1 is a view in perspective of a lithograph blanket in accordancewith the invention;

Fig. 2 is a cross-sectional view taken on line 2-2 of Fig. 1;

Fig. 3 is a cross-sectional view taken transversely through animpression cylinder having a lithograph blanket mounted thereon;

Fig. 4 is an end view and elevation of a device for mounting a blanketon a cylinder and pulling it tautly therearound; and

Fig. 5 is a front view and elevation of a device shown in Fig. 4.

Referring now to the drawings and specifically to Fig. 1, a lithographblanket in accordance with the present invention comprises a rubbersheet II] that is vulcanized to a thin metal sheet II which has its endportions 12 extending beyond the ends of the rubber sheet [0, at leastone of said end portions l2, which forms the front end, havingregistering holes 13 for cooperation with registering pins on animpression cylinder or grinding mandrel, whereas the other end portionl2 need not have the registering holes 13, forming the back end.

The metal sheet ll preferably comprises a copper or zinc copper platedsheet 71000 of an inch thick. Whereas the rubber sheet IE! is ofathickness that will make the thickness of the entire blanket aboutequal or slightly thinner than the regular lithograph blanket. It isobvious that a blanket of this type is absolutely non-stretchable due tothe metal backing and furthermore, it has the additional advantage ofproviding a greater printing area for a given size of the blanket due tothe thinness of the metal backing. V 7

As an example of this latter feature, reference will be made to thedimensions of a standard size of lithograph press which compresses animpression cylinder I5, as shown in Fig. 3, which has the blanketwrapped therearound with the metal backing ll against the surface of thecylinder and the rubber sheet It) to the outside. The cylinder isprovided with a slot l6 to receive 4 the inturned end edges 12 of themetal backing II, and which are retained in the slot by a wedge or barH.

In one standard size machine this impression cylinder with the blanketthereon has a total circumference of approximately 8 /2" whereas theactual printing surface around the cylinder is approximately 8 In usingthe regular prior art canvas-backed blanket, the slot [5 had to be inthe neighborhood of of an inch wide in order to receive the two ends ofthe blanket and a lock bar or wedge II.

This regular blanket is in the neighborhood of 0 of an inch thick sothat the two ends made a total of %000" in all and the wedge or look baris in the neighborhood of of an inch thick making a total of as theminimum necessary width of the slot I6. In using a blanket of thepresent invention however the total thickness of the ends I2 and the barI? amounts to so that the slot 16 can be smaller and increase theprinting circumference of the impression cylinder. Furthermore, thetotal thickness of the metal backing H and rubber sheet IE3 need only be40-45 thousandths of an inch thick so that the cylinder l5 may be 2.61inches in diameter to bring the total diameter with the blanket thereonup to 2.7, which is the diameter of the printing surface of the cylinderin this specific press. On the other hand, with the prior art blanket,which is in thickness, the cylinder had to be 2.57 and the opening orslot I6, .270" wide which reduced the effective printing area to lessthan 8" at the edge of the rubber when clamped in place. Whereas the newmetal backed blanket being cut back on each edge to provide clearness ofthe bends in the metal at each end, the printing surface results in anarea of 8.168.

Thus it will be seen that the metal backing not only provides anon-stretchable blanket but permits a thinner blanket occupying less ofthe available cylindrical surface in being clamped to the impressioncylinder and providing a larger actual printing area. In order to obtaina blanket of absolutely uniform thickness it is necessary to grind thesurface of the rubber sheet Ill. Further, the grinding action of thesurface creates a superior printing or transfer surface, for receivingand ofi-setting the image.

It has been found that superior results in the grinding operation areobtained by mounting the blanket on an arbor and grinding it in a latherather than grinding it in a plane. When the blanket is pulled tautaround a cylindrical surface the rubber layer to the outside of theblanket is stretched slightly and positioned under substantially thesame conditions as in use whereas when flat the rubber is not stretchedand has greater elasticity, so that it tends slightly to be forced aheadof the grinding wheel particularly in the thicker spots. Obviously withthe prior art offset blankets which are canvas-backed, they are not truein the first place and further, it is impossible to grind themaccurately regardless of their being mounted cylindrically or on theflat as the thicker layer of rubber permits greater deformation duringthe grinding operation-and the canvas-backing permits stretching to asufiicient degree to throwthe entire blanket off.

In forming the present blanket, however, it is cutto the required sizeboth as to the rubber printing sheet Ill and the metal backing H witheczema.

the projecting ends l2. The front or leading edge "wouldbe cut toprovide the registering edge which is used to locate the blanket so thatthe ends would be correctly formed. It is obvious that these ends can bealike, as shown in Fig. l or may be flush with the rubber and used inthe same manner as prior art blankets although the projecting metal"ends are preferred,

Togrind the blanketit is mounted on a cylinder 2!! which is best shownin Fig. 4. The cylinder preferably comprisesa cylindrical shell 2|mounted on a shaft 22and having a cutaway open side 23 to accommodate atransversely extending bar 24 supported at its ends by radiallyextending arms 25 which arepivotally mounted on the shaft22, beyond theends of the cylindrical mandrel. One edge portion 25 of the cylindricalsurface of the mandrel 2| isb'evelled to accommodate clamps 2? withinthe circumference of themandrel. The clamps 21 are for securing thefront registering end 52 of the blanket to the cylinder and cooperatewithpins 28 extending through the registering holes It for registeringthe front end of the metal backing sheet H. The clamps27 are secured byscrews 23.

When the blanket is Wrapped around the mandrel 2|, the opposite endportion I2 is located adjacent the other edge of the cutaway portion 23and may be clamped to the transverse bar 24 by clamps 2i) and screwsSfi.One or more bolts 3| are threaded through the bar 24 to abut thesubstantially radial edge 32 of the cutaway portion 23 of the cylinder2|, so that, after the blanket end I2 is clamped to the transverse bar24,the bolt 3| may be screwed to bear against the hear-- ing surface 32to pull the blanket taut around the cylindrical mandrel 2 In ordertoexpedite the mounting of the blanket on the cylinder 2| and securesufficient tautness thereon, the cylinder is preferably mounted in astretching device comprising abase member 35 having upstanding sidemembers 36 which are provided with U-shaped bearing brackets 31 forremovably receiving the shaft ends 22. The side members 35 also includesleeve bearings 38 which receive a cross shaft 39 that carries, and isfixed to, a pair of arms 49 which are adapted to overlie the cylinder 2I.

These arms 40 have bearings 4| for receiving and carrying a cross-shaft42 and terminate in longitudinal extending handles 43. The shaft 42carries a pressure roller 44 for bearing on the blanket as the cylinder2| is rotated. The pressure roller 44 is frictionally restrained fromrotation by a brake drum 45 carried by the shaft 42 at one end beyondone of the arms 40 as best shown in Fig. 5. A pair of arched brake shoes46 straddle the drum 45 and are pivo-tally mounted on the adjacent arm49 by a pin 41. The tension of the brake shoes 46 is regulated by a bolt48 extending freely through a bore 49 in one of the shoe members andthreading into a bore 50 in the other of the shoe members, a spring 5|being coiled about the bolt 48 between its head and the free shoe memberso that, depending upon the threading of the bolt relative to the bore50 of the shoe member, the tension of the spring 5| will be varied toregulate the pressure between the shoes 46 and the frictional resistanceapplied to the brake drum 45. Obviously, the drum 45 and/or the brakeshoes 46 may be provided with suitable brake linings such as leather orthe like.

The arms 40 are connected to the shaft 39 by a tapered pin 52 extendingdiametrically throu h pin holes 53 in the arms 40 and a pin hole 54 inthe shaft 39. The pin holes 53 or the arms 40 are slightly larger thanthe pin 52 to allow a slight play therebetween and to permit slightangular adjustment between the arms so that the pressure roller 44 willcontact the blanket on the cylinder 2| regardless of any variations ofthickness of the blanket between the sides thereof. Thearms 45 terminatein extensions 55 having bearings 56 for receiving pins 57 whichpivotally support telescoping rods 58 that are pivoted by pins '59, inbearings 65, to the side members 36. Each telescoping rod 58 has acollar 6|, or other suitable stop member, on its upper portion and issurrounded by a helical spring 52 compressed between the collar 5! and abearing portion 53 at its lower end so that the rod is resilientlybiased in extended position to hold the arms 45 in their extremepositions but may be resiliently compressed to permit a pivoting of thearms 49 from one position to the other.

In mounting a blanket on the cylindrical mandrel 2|, the arms 45 areswung to their upper positions shown in dotted line in Figure 4 andretained by the resilient telescoping rods 55. The

mandrel 2| is mounted in the device by seating position of the cylinder.The blanket is mounted on the mandrel 24, the end portion l2 beingregistered therewith by inserting the pins 23 off'the mandrel in theholes l3 of the blanket and then securing the end portion i2 by theclamp .21.

The arms 49 are then swung down so that the pressure roller 44 engagesthe leading edge of the blanket adjacent the clamp 21, and the bolt 48may be threaded to adjust the frictional tension between the .brakeshoes45 and the drum 45. The cylinder 2| is then rotated while the pressureroller 44 bears against the blanket and irons it out by pullingthe'blanket tightly about the cylinder 2| due to its retarded rotationthrough its brake. The pressure roller 44 engages the surface of theblanket regardless of the variations in blanket thickness due to thelimited play between the arms that is permitted by the enlarged pinholes 53, and the individual tension rods 58 of each of the arms.

When the cylinder 2| is rotated until the opposite end of the blanket isadjacent the pressure roller 44 the blanket is pulled taut around thedrum and its opposite end I2 may be clamped to the cross bar 24, if ithas not previously been clamped thereto. The one or more bolts 3| maythen be threaded against the bearing surface 32, to space the bar 24from the surface 32 and hold the blanket in taut position about thecylinder 2|. The arms 40 may then be raised and the cylindrical mandrel2| removed from the bearing sockets 31 and placed in a suitable lathe orgrinding machine to grind the rubber surface of the blanket touniformity.

Although a certain specific embodiment of the invention has been shownand described, it is obvious that many modifications thereof arepossible. The invention, therefore, is not to be restricted except bythe spirit of the appended claims.

What I claim as new, is:

l. Adevice for wrapping a blanket on a form and pulling said blankettaut thereon, which device comprises a support, a cylindrical formjournalled on said support, means on said form for removably securingthe ends of a blanket thereto, a pressure roller rotatably carried bysaid support, means for pressing said roller toward said form forengaging a blanket on said form, and means for retarding rotation ofsaid pressure roller to create a drag as well as a pressure for pullingsaid blanket taut as said roller moves relative to said blanket.

2. A device as set forth in claim 1 wherein said roller pressing meanscomprises resilient means individually creating a pressure on each endof said roller to accommodate variances in thickness of the blanket.

3. A device for wrapping a blanket on a form and pulling said blankettaut thereon, which device comprises a support, a cylindrical formjournalled on said support, means on said form for removably securingthe ends of a blanket thereto, a frame pivotally mounted on said supportand having a free end movable to and from a position overlying saidcylindrical form, a pressure roller rotatably supported by said freeend, means for biasing said frame toits extreme positions so that whenthe free end thereof overlies said cylindrical form the roller thereonwill press against a blanket mounted on said form, and a brake to retardrotation of said roller and thereby create a drag on the blanket as theform is rotated.

' 4. A device for wrapping a blanket on a form and pulling the blankettaut thereon, which device comprises a support adapted to rotatablysupport a cylindrical blanket carrying form, a frame pivotally mountedon said support and havinga free end movable to and from a positionoverlying the position of the cylindrical form, a. pressure rollerrotatably supported by said free frame end, means biasing said frame toits extreme positions so that when the free end thereof overlies thecylindrical form said roller will press against a blanket mounted onsaid form, the sides of said frame being independent and each said sidebeing independently journalled and having a limited freedom of movementto permit angular variations of the axis of the roller whereby toaccommodate variances in thickness of the blanket.

6. A device as set forth in claim 5, wherein said biasing meanscomprises resilient means biasing each side of said frame independently.

'7. A device as set forth in claim 5, wherein the roller is providedwith a brake to retard rotation thereon and create a drag on theblanket.

8. A device for wrapping a blanket on a form and pulling the blankettaut thereon, which device comprises a support adapted to rotatablysupport a cylindrical blanket carrying form, a frame pivotally mountedon said support and having a free end movable to and from'a positionoverlying the position of the cylindrical form, a pressure rollerrotatably supported by said free frame end, means biasing said frame toits extreme positions so that when the free end thereof overlies thecylindrical form said roller will press against a blanket mounted onsaid form, and a brake for said roller to retard rotation thereof andcreate a drag on the blanket.

WALTER H. SMITH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 629,916 North Aug. 1, 18991,411,707 ,Cannins Apr. 4, 1922 1,555,105 Daushmann Sept. 29, 19251,594,526 Hume Aug. 3, 1926 1,704,563 English Mar. 5, 1929 1,768,681Gollwitzer July 1, 1930 2,051,511 Finch Aug. 18, 1936 2,275,218 ChambersMar. 3, 1942 2,276,012 Blackley Mar. 10, 1942 2,346,468 Brickman et alApr. 11, 1944

